import java.util.Scanner;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: 28779
 * Date: 2023-10-20
 * Time: 20:45
 */

//练习题
public class Text {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        int month = in.nextInt();

        int sum = 1;
        int j = 3;
        int[] count = new int[100];
        for (int i = 1; i <= month; i++) {
            if(i == 1) {
                count[1] = 0;
            } else if(i == 2) {
                count[2] = 0;
            } else if (i == 3) {
                count[3] = 1;
            } else if (i >= 4) {
                count[i] = count[j] + count[j - 1];
                j++;
            }
            sum += count[i];
        }
        System.out.println(sum);
    }
}
